1. Field of the Invention
The present invention relates to a read head having a read sensor overlaid with reactive-ion-etch defined lead layers and a method of making and, more particularly, to first and second overlaying lead layers which overlay first and second spaced apart top surface portions of the read sensor with the first and second overlaying lead layers mainly providing sufficient shunting of a sense current to render side portions of the read sensor below the overlaying lead layers inactive.
2. Description of the Related Art
The heart of a computer is a magnetic disk drive which includes a rotating magnetic disk, a slider that has a magnetic head assembly including write and read heads, a suspension arm above the rotating disk and an actuator arm. The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent an air bearing surface (ABS) of the slider causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing the actuator arm swings the suspension arm to place the write and read heads over selected circular tracks on the rotating disk where signal fields are written and read by the write and read heads. The write and read heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
An exemplary high performance read head employs a giant magnetoresistance (GMR) read sensor for sensing magnetic signal fields from the rotating magnetic disk. The GMR read sensor comprises seed layers, a nonmagnetic electrically conductive spacer layer that is sandwiched between a ferromagnetic pinned layer and a ferromagnetic sense layer, and cap layers. An antiferromagnetic pinning layer interfaces the pinned layer for pinning the magnetization of the pinned layer 90° to an air bearing surface (ABS) wherein the ABS is an exposed surface of the read sensor that faces the rotating disk. First and second hard bias and tapered lead layers are connected to the read sensor for conducting a sense current therethrough. The magnetization of the sense layer is free to rotate upwardly and downwardly with respect to the ABS from a quiescent or zero bias point position in response to positive and negative signal fields from the rotating magnetic disk. The quiescent position of the magnetization of the sense layer, which is parallel to the ABS, is when the sense current is conducted through the read sensor without signal fields from the rotating magnetic disk.
When a sense current is conducted through the read sensor, electrical resistance changes cause potential changes that are detected and processed as playback signals. The sensitivity of the read sensor increases with a giant magnetoresistance (GMR) coefficient ΔR/R where ΔR is the change in resistance of the read sensor from minimum resistance (when magnetizations of sense and pinned layers are parallel to each other) to maximum resistance (when magnetizations of the sense and pinned layers are antiparallel to each other) and R is the resistance of the read sensor at minimum resistance.
First and second hard bias and tapered lead layers are connected to first and second side surfaces of the read sensor, which connection is known in the art as a contiguous junction. This contiguous junction is described in commonly assigned U.S. Pat. No. 5,018,037 which is incorporated by reference herein. The first and second hard bias layers longitudinally stabilize the magnetization of the sense layer of the read sensor in a single domain state which is important for proper operation of the read sensor. The first and second tapered lead layers are for the purpose of conducting the aforementioned sense current through the read sensor parallel to the ABS and parallel to the thin film interfaces of the read sensor.
Rows and columns of the sliders having magnetic head assemblies are fabricated on a wafer. Each magnetic head assembly is located on a respective slider wherein each slider is a portion of the wafer. After fabricating the rows and columns of the sliders, the wafer is diced into rows of sliders and each row of sliders is then lapped to form the aforementioned ABS. Each row is then diced into individual sliders wherein each slider has a magnetic head assembly with write and read heads exposed at the ABS.
In the fabrication process of the rows and columns of the sliders, the read sensor of the read head and the first and second hard bias and tapered lead layers connected thereto are deposited on the wafer in an integrated ion-beam/DC-magnetron sputtering system. The rows and columns of sliders, where the read sensor and the first and second hard bias and tapered lead layers are to be constructed, are typically located within a square or rectangle on the wafer. The wafer itself is typically circular. After the read sensor, comprising the seed, pinned, spacer, sense and cap layers, are deposited over the entire wafer, the read sensor is then annealed which partially oxidized the top layer of the cap layers. A bilayer photoresist mask is then applied and exposed in a photolithographic tool to mask the read sensor in its central portion and then subsequently developed in a solvent to form undercuts on each side of the bilayer photoresist mask. The read sensor, which is unmasked by the bilayer photoresist mask, is removed by ion milling until the first read gap layer is exposed. The first and second hard bias layers are then deposited so that they abut the first and second side surfaces of the read sensor with tapered portions of the hard bias layers overlaying the read sensor. This step may be accomplished by ion beam sputtering at an angle of 10° while the wafer is rotated. The first and second tapered lead layers are then immediately deposited which interface the first and second hard bias layers as well as extending under the undercuts and tapering toward one another. The first and second tapered lead layers may be deposited by ion beam sputtering also at an angle of 10° while the wafer is rotated. The bilayer photoresist mask is then lifted off.
The prior art process has several disadvantages. One disadvantage is that the partially oxidized portion of the top layer of the cap layers prevents proper electrical contact between the read sensor and the first and second hard bias and tapered lead layers in two side portions of the read sensor. Consequently, the sense current is restricted in its flow from the first and second hard bias and tapered lead layers to the read sensor in the two side portions of the read sensor. Second, due to shadowing effects of the bilayer photoresist mask in the undercuts, it is difficult for the first and second tapered lead layers to penetrate into the undercuts during deposition of the first and second tapered lead layers. This results in thin taper portions formed somewhere uncertainly in the undercuts. These taper portions are so thin that substantial current shunting cannot be attained and the side portions of the read sensor below the undercuts remain active during sensor operation which causes side reading.